How can I avoid jagged edges?
Your compositing nodes are the cause. Because the blend does not have textures packed, I'm not 100% sure why you are compositing it the way you are.
However to fix the harsh edge around the container, simply check the Anti-Aliasing check box on both of the ID Mask nodes.


Here is what the mask looks like Anti-Aliased on the left, and without Anti-Aliasing (how you have it now) no the right.